Anchors with biodegradable constraints

ABSTRACT

An implant includes a collapsible anchor to be deployed within a lumen and a protrusion coupled to the anchor. The protrusion, in a constrained state, extends a distance from an exterior surface of the anchor and, in an unconstrained state, extends further from the exterior surface of the anchor. Also included is a biodegradable constraint, such as a biodegradable tube or suture, configured to maintain the protrusion in the constrained state until the constraint releases. The implant may include additional biodegradable constraints, each constraint configured to maintain the protrusion in a different constrained state and to degrade over a different predetermined period after the implant has been deployed within the lumen. The protrusion may include a bi-directional barb or an open loop. The protrusion may be configured to penetrate a wall of the lumen and to allow tissue to grow about the protrusion. The implant may also include an unsupported, thin-walled sleeve coupled to the anchor and configured to extend into the lumen upon deployment of the collapsible anchor.

RELATED APPLICATIONS

This application is a continuation-in-part of International ApplicationNo. PCT/US2010/048444, which designated the United States and was filedon Sep. 10, 2010, which claims the benefit of U.S. ProvisionalApplication No. 61/276,381, filed on Sep. 11, 2009 and U.S. ProvisionalApplication No. 61/361,806, filed on Jul. 6, 2010.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Obesity is associated with a wide variety of health problems, includingType 2 diabetes, hypertension, coronary artery disease,hypercholesteremia, sleep apnea, and pulmonary hypertension. It alsoexerts an enormous strain on the body that affects the organs, thenervous system, and the circulatory systems. Obesity rates have beenrising for years in the United States, causing corresponding increasesin healthcare expenditures.

Curing obesity has so far vexed the best efforts of medical science.Dieting is not an adequate long-term solution for most obese people,especially those with a body-mass index of over 30. Stomach stapling, orgastroplasty, reduces the size of the stomach, leading to reducedappetite and weight loss, but eventually the stomach stretches and thepatient's appetite returns to pre-surgery levels. Roux-en-Y gastricbypass reduces the size of the stomach and the length of the intestine,and leads to both weight loss and alleviation of the Type 2 diabetescommon to obese patients. Although gastric bypass appears to provide amore permanent solution than gastroplasty, complication rates associatedwith gastric bypass are between 2% and 6%, with mortality rates of about0.5-1.5%.

Endoscopically delivered gastrointestinal implants, such as thosedescribed in commonly assigned U.S. Pat. Nos. 7,025,791 and 7,608,114 toLevine et al., incorporated herein by reference in their entireties,provide the benefits of gastric bypass without the hazards of surgery.For example, an implant may include a thin-walled, floppy sleeve that issecured in the stomach or intestine with a collapsible anchor. Thesleeve extends into the intestine and channels partially digested food,or chyme, from the stomach through the intestine in a manner that maycause weight loss and improve diabetes symptoms. The sleeve and anchorcan be removed endoscopically when treatment is over or if the patientdesires.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide improved anchoring of animplant in the gastrointestinal tract and can increase the duration thatan implant can be anchored in the intestine by providing biodegradableconstraints that maintain anchoring protrusions in a constrained stateuntil the constraint releases.

An implant according to the principles of the invention includes acollapsible anchor to be deployed within a lumen and a protrusioncoupled to the anchor. The protrusion, in a constrained state, extendsbetween about 2 mm and about 4 mm from an exterior surface of the anchorand, in an unconstrained state, extends further from the exteriorsurface of the anchor. Also included is a biodegradable constraint, suchas a biodegradable tube or suture, configured to maintain the protrusionin the constrained state until the constraint releases.

The biodegradable constraint typically covers at least a portion of theprotrusion, such as the mid-portion, and may further cover a portion ofthe anchor. The implant may include additional biodegradableconstraints, each constraint configured to maintain the protrusion in adifferent constrained state and to degrade over a differentpredetermined period after the implant has been deployed within thelumen. The protrusion may include a bi-directional barb, an open loop,and/or a helix and may be configured to penetrate a wall of the lumen.The protrusion can be coupled to the anchor between ends of the anchor.In an embodiment, the protrusion extends between about 4 mm and 8 mmfrom the exterior surface of the anchor when released from theconstrained state.

A method of securing a collapsible anchor within a lumen includesdeploying the collapsible anchor within the lumen, the collapsibleanchor having a protrusion that, in a constrained state, extends betweenabout 2 mm and about 4 mm from an exterior surface of the anchor.Further, the method includes maintaining the protrusion in theconstrained state with a biodegradable constraint and penetrating a wallof the lumen with the protrusion in the constrained state to secure theanchor.

The method may include allowing tissue to grow about the protrusion.Further, the method may include allowing the biodegradable constraint todegrade over a predetermined period after the implant has been deployedin the lumen to release the protrusion from the constrained state.Further yet, the method may include bending the protrusion alongside thecollapsible anchor to place the protrusion in the constrained state andinserting the protrusion, in the constrained state, into the lumen.

The collapsible anchor, which may, for example, be a wave anchor or astent comprising a network of struts, is configured to be deployedwithin a lumen in a mammalian body. Upon deployment, the collapsibleanchor expands within the lumen, and the protrusion, when released,expands away from the anchor, pushing the protrusion against the wall ofthe lumen. In some embodiments, the protrusion has a first end coupledto the anchor and a second end formed in an open loop. Over time, theprotrusion and, if present, the open loop penetrate the luminal wall,and the protrusion and/or the open loop, may project through the farside of the luminal wall. A pocket of scar tissue forms about the openloop and through an opening in the open loop, securing the anchor withinthe lumen. The implant may have additional protrusions, each of which isconnected to the anchor and can include an open loop. Each additionalopen loop also includes an opening and is adapted to penetrate theluminal wall upon deployment of the collapsible anchor.

Each open loop may have an inner opening with a width of between about 1mm and about 13 mm, or, more preferably, an inner diameter of about 3mm. Typically, the protrusion extends along a total length of betweenabout 6 mm and about 13 mm from the collapsible anchor upon fulldeployment from the collapsible anchor. The protrusion and the open loopmay be formed of wire (e.g., nitinol wire) with a preferred diameter ofabout 0.010 inch to about 0.040 inch, and more preferably about 0.020inch.

The open loop can be formed of a loop of wire, and the protrusion can beformed of a straight length of wire extending from the loop of wire. Theopen loop may be oriented in a variety of directions with respect to thecollapsible anchor. For example, the open loop may define a plane thatis perpendicular to the lumen wall when the protrusion is deployed.Alternatively, the open loop may define a plane that is parallel to thelumen wall when the protrusion is deployed. When the protrusion is in acollapsed state, it folds against or along the side of the collapsibleanchor. When relaxed or unconstrained, straight protrusions typicallyextend outwards from the collapsible anchor at an angle of between about45 degrees and about 135 degrees, or, more preferably, to an angle ofabout 80 degrees or about 90 degrees. At these angles, the expandedstraight protrusion pushes the loop outward, causing an edge of the loopto engage the luminal wall.

Alternatively, the protrusion can include a length of wire formed in ahelix. The wire used to form the helix may be coiled to form the loop,which can be oriented such that it is parallel to the luminal wall whendeployed within the lumen. (Other orientations of the loop are alsopossible.) The helix may have a tapered profile (e.g., a conicalprofile) when viewed from the side, and can be flattened alongside thecollapsible anchor. The collapsed implant can be inserted into the lumenendoscopically. Releasing the helix and the anchor from the collapsedstate causes the helix to push the loop away from the anchor, which, inturn, causes a face of the loop to engage the luminal wall. The implantmay also include an end effect at or near the tip of the loop to aidpenetration of the loop through the luminal wall.

The implant can be collapsed, for removal from the lumen, with anoptional drawstring that runs through the opening in the loop or throughadditional retaining hooks or loops connected to the loop or theprotrusion. Pulling on the drawstring collapses the loop and protrusiontowards the collapsible anchor, and away from the luminal wall.Collapsing an implanted helix may cause coils in the helix to shearfibrotic tissue formed about the helix depending on the spacing andorientation of the coils that make up the helix.

An implant with a protrusion can also include an unsupported,thin-walled sleeve coupled to the collapsible anchor and configured toextend into the lumen (e.g., the intestine) upon deployment of thecollapsible anchor. The implant may also include a restrictor plateinstead of or in addition to the thin-walled sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIGS. 1A-1D are perspective, plan, and elevation views of straightprotrusions with open loop s coupled to a wave anchor.

FIGS. 2A-2C illustrate how a straight protrusion with an open loopextends further from the anchor as biodegradable constraints release.

FIGS. 3A-3C illustrate how a straight protrusion with an open looppenetrates the wall of the gastrointestinal tract and how a fibroticencapsulation forms about and through the open loop.

FIGS. 4A-4B are perspective views of wave anchors with helicalprotrusions with open loops.

FIG. 5 is a perspective view of a loop projection with a helical neckand a biodegradable restraint.

FIGS. 6A-6C illustrate how a helical protrusion with an open loopextends upon release of a biodegradable restraint and penetrates thewall of the gastrointestinal tract.

FIGS. 7A-7D show compound barb protrusions in un-constrained andconstrained states.

FIGS. 8A-8B illustrate how the tissue responds to a conventional barbpenetrating the wall of the gastrointestinal tract.

FIGS. 8C-8D illustrate how tissue responds to a compound barbpenetrating the wall of the gastrointestinal tract and further extendingupon release of a biodegradable restraint.

FIG. 9A shows an implant that includes a sleeve extending from an anchorwith open loop protrusions maintained in a constrained state bybiodegradable constraints.

FIG. 9B shows and implant that includes a sleeve extending from ananchor with compound barb protrusions maintained in a constrained stateby biodegradable constraints.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A description of example embodiments of the invention follows.

An anchor may be used to secure a sleeve in the intestine of a patientfor treating obesity and/or type-2 diabetes as described in commonlyassigned U.S. Pat. No. 7,025,791; U.S. Pat. No. 7,608,114; U.S. Pat. No.7,476,256; U.S. Pat. No. 7,815,589; U.S. patent application Ser. No.11/330,705, filed on Jan. 11, 2006, by Levine et al.; U.S. patentapplication Ser. No. 11/827,674 filed on Jul. 12, 2007, by Levine etal., all of which are incorporated herein by reference in theirentireties.

As described in the above-referenced patents and patent applications,straight, sharp barbs fixed to a self-expanding anchor may be used tosecure an implant to the duodenal wall. However, the body's healingresponse stimulates a progressive tissue proliferation around sharpbarbs in response to the injury caused as the anchor pushes the sharpbarbs into the wall of the duodenum. The inflammatory response to theinjury produces a mix of granulation and more stable fibrous tissue(i.e., scar tissue). This causes thickening of the duodenal wall overtime resulting in barbs disengaging from the tissue. Typically, thethickening of the duodenal wall is the result of infiltration of lessstable, granulation tissue such that the tissue closest to the lumen isnot very tough or stable. The thickening of the wall leads to the barbsdisengaging from the muscle layer or the fibrotic scar tissue whilestill residing in the less stable, granulation tissue. As sharp barbsseparate from the duodenal wall, the implant may become unstable andmigrate or rotate within the duodenum.

Long barbs or protrusions tend to be better than short barbs orprotrusions at holding implants securely for longer periods. Withoutsubscribing to any particular theory, it appears that longer barbs orprotrusions are more stable because it takes more time for theinflammatory thickening to separate longer barbs or protrusions from themuscle layer. However, there is a practical limit to how long sharpbarbs can be because longer sharp barbs are more likely to infiltratesurrounding organs. Very long sharp barbs or long protrusions can pierceor erode through the muscle wall of the intestine and into adjacentstructures and could potentially cause leaks, bleeding, or adhesions toother organs.

Protrusions with open loops (also called open heads), on the other hand,can secure an implant for longer periods of time while minimizing therisk of damage to nearby organs. In addition, protrusions or barbs canbe deployed in a constrained state, e.g. having reduced barb height, toinitially secure the anchor in the wall of the duodenum, and thenreleased to an un-constrained state, e.g. having lengthened barb height,after a predetermined period of time to further improve anchoringstability. Deploying an implant having smaller barb heights can avoidcomplications with adjacent anatomy and facilitate packaging of theimplant during endoscopic delivery. The ability to increase the barbheight after implantation and in response to the natural healingmechanism of thickening of the duodenal wall allows for increasedanchoring stability.

In one embodiment, the protrusion, which is relatively narrow (e.g.,about 0.060 inch wide) and relatively long (e.g., about 13 mm long),connects a relatively broad open loop (e.g., about 3 mm in diameter) toa collapsible anchor. Upon deployment, the protrusion pushes the openloop against the intestinal wall. Without being bound by any particulartheory, initial research suggests that the muscle layer in the intestinestretches across the loop, and it eventually thins out or erodes enoughto allow the loop to penetrate the luminal wall. A chronic inflammationresponse causes scar tissue to form around the loop and through theopening formed by the loop; this scar tissue can hold the loop securely.Because the loop is rounded or otherwise shaped to promote erosionthrough the muscle wall, the protrusion and the loop are less likely topierce the scar tissue or surrounding organs.

Straight Protrusions with Open Loops

FIGS. 1A-1D show an implant 100 suitable for deployment within thegastrointestinal tract distal to the pylorus. The implant 100 includes acollapsible wave anchor 102 that includes a plurality of protrusions110, each of which extends outward from the wave anchor 102. FIGS. 1A-1Cshow perspective, plan, and elevation views of the implant 100 in arelaxed state with protrusions 110 in an unconstrained state (from thetop, the relaxed implant 100 looks circular); FIG. 1D is an elevationview of the implant 100 in a compressed state with protrusions 110 in aconstrained state. As shown, protrusions 110 extend from the anchor 102in the constrained state and extend further from the anchor in theun-constrained state. Typically, the implant 100 is compressed forendoscopic deployment within the gastrointestinal tract and insertedwith the protrusions maintained in a constrained, or collapsed, state.Once positioned properly within the gastrointestinal tract, the implant100 expands to the relaxed state shown in FIGS. 1A-1C. The protrusions110, however, may be maintained in a constrained state, such as shown inFIG. 1D, until released after a predetermined period of time after theimplant has been inserted in the gastrointestinal tract.

The anchor 102 may have a relaxed diameter of about 40 mm or greater,e.g., about 45 mm, about 50 mm, or about 55 mm. Each protrusion 110includes a rounded loop 112 at the end of a narrow, straight neck 114,and each loop 112 includes an opening whose inner width D is within therange (inclusive) of between about 1 mm and about 13 mm, and preferablya diameter D within a range of about 1 mm and about 6 mm, or, morepreferably, about 3 mm. The outer diameter can be within a range ofabout 2 mm to about 8 mm, and the diameter of the wire used to form eachprotrusion 110 can be within a range of about 0.010 inch to about 0.030inch. Typically, the minimum bend radius of the wire limits the minimuminner diameter (it can be difficult to bend the wire too tightly), andthe minimum desired pressure exerted by the loop 112 against the tissuelimits the maximum inner diameter (bigger loops 112 may not exert enoughpressure on the tissue to penetrate the tissue). The straight neck 114has a length l of between about 6 mm and about 10 mm, for a totalprojection length L of between about 7 mm and about 13 mm. A crimp 116or other suitable connection fixes the neck 114 to the wave anchor.

Each protrusion 110 folds down along the side of the wave anchor 102when compressed for delivery. A biodegradable constraint 144, such as abiodegradable tube or suture, maintains the protrusions in a constraintstate until the constraint releases. The protrusion, in a constrainedstate, may extend at least about 2 mm, e.g., between about 2 mm andabout 4 mm, from an exterior surface of the anchor 102 and, in anunconstrained state, extend further from the exterior surface of theanchor. Each protrusion 110 may spring up to extend nearlyperpendicularly from the wave anchor 102 when released from thecompressed state to the relaxed or un-constrained state. Specifically,the angle φ formed by the protrusion 110 and a leg of the wave anchor102 may be between about 45° and about 135°, or, more preferably,between about 75° and 105°, e.g., about 80° or about 90°.

For example, the biodegradable or erodible constraint 114 can be formedfrom PolyLactide (PLA), PolyGlycolic Acid (PGA), poly(lactic-co-glycolicacid) (PLGA), or any other material that degrades when implanted in thestomach or intestine. Materials used for sutures, such as silk, aresuitable biodegradable materials for constraint 114. Another suitablematerial is polyethylene terephthalate (PET), which is commonly used forbeverage containers and may degrade over a relatively long period oftime after implantation. Different biodegradable materials differ intheir degradation profile. For example, the duration over which amaterial degrades can range from hours to years and depends on multiplefactors, including the environment to which the material is exposed. Thedegradation may occur according to a hydrolytic reaction, where wateracts as a catalyst, or may occur in an acid based reaction.

Some biodegradable materials, such as PGLA, offer the advantage of alsobeing bioresorbable (also referred to as bioabsorbable). In one example,a biodegradable constraint is a tube formed from PLGA, a bioresorbablepolymer, which may be made using PLGA tubing available under the ZEUS®ABSORV PLGA brand. In another example, a biodegradable constrainingelement is formed using a bioresorbable suture. Advantageously,depending on the configuration of the biodegradable material, theconstraint 114 can be formed to degrade after a predetermined period ofimplantation. At the predetermined period of time, preferably after theinitial inflammatory response of the duodenal wall, the biodegradableconstraint 114 dissolves allowing the protrusion to reach its fullheight, thereby providing additional stability in the duodenal wall.

In one example, an open loop protrusion 110 is formed of a single pieceof nitinol wire with a diameter of about 0.020 inch. The wire is bent toform a pair of struts that can be crimped, bonded, or welded onto asingle-wire leg of an anchor (e.g., wave anchor 102 in FIGS. 1A-1D) suchthat the single wire of the anchor leg nestles between the struts. Thewire is bent to form the narrow, straight neck 114 and coiled twice tocreate the loop 112. The two loops of coil form a broad, blunt edge thatcan engage and erode the luminal wall such that the loop 112 eventuallypenetrates the luminal wall. Further details of the open loop protrusionare described in International Application No. PCT/US2010/048444, filedon Sep. 10, 2010, which is incorporated by references in its entirety.

FIGS. 2A-2C illustrate how a straight protrusion 110 with an open loop112 extends incrementally further from the anchor 102 as biodegradableconstraints 244, 244′, and 244″ release. Each constraint is configuredto maintain the protrusion in a different constrained state and todegrade over a different predetermined period after the implant has beendeployed within the lumen. As shown in FIG. 2A, constraints 244, 244′,and 244″ wrap around neck 114 of protrusion 110 and around a strut ofanchor 102. Each biodegradable constraint 244, 244′, and 244″ can be asuture that ties a portion of the protrusion 110 to a portion of theanchor 102, thereby maintaining protrusion 110 in respective constrainedstates. Different thicknesses of constraints 244, 244′, and 244″ aremeant to illustrate that the constraints are configured to degrade atdifferent periods of time. As shown, thin suture 244 is configured todegrade first, medium thickness suture 244′ next, and thick suture 244″last. Alternatively or in addition, constraints or sutures 244, 244′,and 244″ may be formed from different biodegradable materials thatdiffer in their respective degradation profiles.

FIG. 2A shows the implant 100 in a first constraint state with allconstraints 244, 244′, and 244″ present. The implant 100 may for examplebe in this first constrained state immediately after deployment into thelumen. As shown, constraint 244 maintains protrusion 110 in the firstconstrained state such that protrusion 110 and a leg of the wave anchor102 form angle φ₁. The combination of the angle φ₁ and the length ofprotrusion 110 results in protrusion 110 extending from the anchor 102for a total projection length L₁. As shown, L₁ is measured from thesurface of anchor 102 to loop 112 of protrusion 110. Constraints 244′and 244″ may or may not cooperate with constraint 244 to maintainprotrusion 110 in the first constrained state. As shown in FIG. 2A,constraints 244′ and 244″ form loose loops around neck 114 of protrusion110 and anchor 102. In this example, the loose loops formed byconstraints 244′ and 244″ do not constrain protrusion 110.

FIG. 2B shows the implant 100 in a second or intermediate constraintstate after constraint 244 has degraded and implant 100 was releasedfrom the first constrained state. Only constraints 244′ and 244″ remainin the second constrained state. The implant 100 may for example be inthis second constrained state after the luminal wall has responded tothe implant with inflammatory tissue growth as described elsewhereherein. As shown, constraint 244′ maintains protrusion 110 in the secondconstrained state such that protrusion 110 and a leg of the wave anchor102 form angle φ₂. The combination of the angle φ₂ and the length ofprotrusion 110 results in protrusion 110 extending from the anchor 102for a total projection length L₂. Preferably, angle φ₂ is greater thanangle φ₁ and projection length L₂ is greater than projection length L₁.Constraint 244″ may or may not cooperate with constraint 244′ tomaintain protrusion 110 in the second constrained state. As shown inFIG. 2B, constraint 244″ is a suture that forms a loose loop around neck114 of protrusion 110 and anchor 102. In this example, the loose loop ofthe suture does not constrain protrusion 110.

FIG. 2C shows the implant 100 in a third or final constraint state afterconstraint 244′ has degraded and implant 100 was released from the firstand second constrained states. Only constraint 244″ now remains to keepprotrusion 110 in the third constrained state. The implant 100 may forexample be in this first constrained state immediately after deploymentinto the lumen. As shown, constraint 244′ maintains protrusion 110 inthe second constrained state such that protrusion 110 and a leg of thewave anchor 102 form angle φ₂. The combination of the angle φ₃ and thelength of protrusion 110 results in protrusion 110 extending from theanchor 102 for a total projection length L₃. Preferably, angle φ₃ isgreater than angles φ₁ and φ₂ and projection length L₃ is greater thanprojection lengths L₁ and L₂.

FIGS. 3A-3C illustrate how the implant 100 is secured within a lumen bya protrusion 110 with a relatively straight neck 114. First, the implant100 is inserted into the lumen in a compressed state, with theprojection 110 folded against the collapsed anchor 102. Once releasedinto the lumen, the anchor 102 and the protrusion 110 expand towardtheir respective relaxed states, causing the edge 124 of the loop 112 toform a tent 309 in the luminal wall 301, which may include a musclelayer, as shown in FIG. 3A. Without being bound by a particular theory,initial studies suggest that, over time, the tent 309 stretches and theface 124 erodes at the point of contact 303, as shown in FIG. 3B.Eventually, the loop 112 erodes completely through the luminal wall 301,as shown in FIG. 3C. Within two to four weeks, fibrotic tissue 305 formsabout and through the loop 112, securing the loop 112 with respect tothe luminal wall 301, and may secure the loop 112 in a permanent orquasi-permanent fashion (e.g., for months or years). A loop 112 that issecured in a pocket of fibrotic tissue 112 does not appear to provokethe tissue remodeling that eventually forces other projections, such assharp protrusions, out of the intestine.

Open-loop protrusions of different shapes are described in InternationalApplication No. PCT/US2010/048444, filed on Sep. 10, 2010, andincorporated by reference in its entirety. For example, a protrusion canbe formed by bending wire into the shape of the Greek letter omega, Ω orby twisting wire into a loop. Protrusions may be separate pieces of wirebonded to an anchor or they may be formed of the same piece of wire thatforms the anchor. An open-tip protrusion may include an erodible orbiodegradable section that forms part of a loop connected to an anchorwith a straight neck. The erodible section dissolves, turning the loopinto an open prong that can be removed from tissue without tearing thetissue that forms in the opening of the loop due to the inflammatoryresponse of the luminal wall. Typically, the erodible section isdesigned to dissolve during treatment, e.g., over six months, one year,two years, or possibly longer. A protrusion may include a corkscrew-likeopen head or a whisk-shaped head perched atop a straight neck coupled toan anchor 102. Tissue may grow about and through the openings betweenthe windings in both the corkscrew-like head and the whisk-shaped head,just as in the helix protrusions described in greater detail below.Protrusion may also be bidirectional and can include a coil-like openhead that engages the luminal wall as the protrusion expands from itsconstrained or collapsed state. The open heads may also be connected tothe anchor with a detachable or erodible feature. For example, a coiledopen loop can be connected to a straight neck with a bio-erodible orbiodegradable element. Upon deployment, the loop erodes through theluminal wall and soon becomes encased in fibrotic tissue, securing theprotrusion and attached anchor 102 in place. Over time, the bio-erodibleelement dissolves, causing the loop to become detached from theprotrusion. Once the head is no longer connected to the protrusion, theprotrusion can be withdrawn without necessarily tearing the scar tissueencapsulating the head, making for easier removal of the implant.

Helical Protrusions with Open Loops

Alternatively, the implant may include a helical protrusion instead of astraight protrusion. The helical protrusion acts as a coil spring thatpushes the open loop into the lumen wall, but in a manner thatdistributes the load from the collapsible anchor to the contactingtissue over a longer length as compared to a straight protrusion ofsimilar height. Upon initial engagement with the duodenal wall, thehelix, if so designed, compresses. As the tissue and helix protrusioncome to equilibrium the helix approaches full expansion, causing theloop to penetrate the luminal wall. Eventually, fibrotic tissueencapsulates the loop and the expanded helix, creating a pocket thatholds the loop and helix securely. Like straight protrusions with openloops, helical protrusions with open heads may be designed forpermanent, quasi-permanent, or temporary implantation. Furthermore, thehelical protrusion can be inserted into the lumen in a constrainedstate. A biodegradable constraint, such as a biodegradable suture, canmaintain the helical protrusion in the constrained state until theconstraint releases.

FIGS. 4A-4B are perspective views of implants that include projectionswith helical protrusion: FIG. 4A shows shows helical protrusions withretaining loops; FIG. 4B shows helical protrusions that includeretaining loops and short end effects that promote initial penetrationof the open loop into the muscle wall. FIG. 4A shows an implant 430 thatincludes five helical protrusions 440, each of which is coupled to awave anchor 102 with a respective crimp 416. (Alternatively, theprotrusions 440 may sutured or releasably coupled to the anchor 102.)Each helical protrusion 440 includes a helix 414 formed of several wirecoils and a loop 412 formed of two loops of wire. The opening of eachhead 412 is parallel to the lumen defined by the wave anchor 102. Eachhelical protrusion 440 has a tapered profile, with the top coils (i.e.,those farthest away from the wave anchor 102) being substantiallysmaller than the base coils (i.e., those closest to the wave anchor102). Each coil in the helix 414 limits the penetration of the coilabove it.

The top coils are sized to focus the force from the expanding implant430 to penetrate the duodenal wall and to ultimately elicit the healingresponse. Top coils approximately 3 mm in diameter are small enough tostart to burrow through the muscle layer. The base coils are larger thanthe top coils and are sized to substantially match and blend to thecrowns (vertices) of the wave anchor 102. For example, a 7 mm diameterbase coil blends well to the wave anchor 102 approximately 6 mm belowthe crowns, but larger base coils could be used for other attachmentconfigurations and/or anchor configurations. Typically, the outerdiameter of the largest coil in the helix 414 is within the range ofabout 1.5 mm to about 12 mm, and the coils have an inner diameter thatranges from about 1.0 mm to about 10 mm The loop 412 can have an innerdiameter within a range of about 1.0 mm and about 6.0 mm.

The spacing of the coils or wire wraps in the helix 414 influences thetissue response. If the coils are too close together, then tissue maynot be able to grow around the wire or between the coils. If the coilsare too far apart, then each coil may exert more localized force on thetissue, causing the tissue to erode at the point of contact. Inaddition, increasing the coil spacing makes it more likely that theupper coils will infiltrate surrounding organs. Setting the spacingbetween wraps, or coil pitch, within a range of about 1.0 mm to about4.0 mm (or, more preferably, within a range of about 2.4 mm to about 2.5mm), limits the erosion caused by the upper coils while allowing fortissue encapsulation of helix 414.

In the examples shown in FIGS. 4A-4B, the loop 412 is formed of twocoils of uniform diameter that are stacked upon each other,approximating a solid cylinder that does not compress. Because the loop412 is relatively incompressible, it erodes through the duodenal wall,but only to an extent determined by the length and compliance of thehelix 414. A helix 414 with appropriate compliance typically preventsthe loop 412 from penetrating much beyond the muscle layer of theduodenal wall.

FIG. 4A shows implant 430 with several projections 440, each of whichincludes a retrieval element 442 that extends from the loop 412 towardsthe wave anchor 102. In the example shown in FIG. 4A, the retrievalelement 442 is a loop of wire formed with an optional hypodermic tube472, which provides an additional surface for fibrotic tissue toencapsulate; this further encapsulation may increase the anchoringstrength. Each retrieval element 442 fits in the conical cavity definedby its associated helical neck 414 and can be used to exert a forcenormal to the axis of the conical cavity on the helical protrusion 410.For example, a normal force can be used to prevent or slow expansion ofthe helical protrusion 410 or to collapse an expanded helical protrusion440. Other retrieval elements may be hooks, balls, or other suitablefeatures for applying a normal force to the helix.

In the example shown in FIG. 4A, a constraint 444 threaded through theretrieval element 442 keeps the helical protrusion 440 in a fully orpartially collapsed state. In some cases, the constraint 444 is a sutureor biodegradable element that allows the user to influence how quicklythe helical protrusion 440 expands after implantation, which, in turn,affects how quickly the loop 412 penetrates the luminal wall. Releasingtension on the suture or engineering the decay time of the biodegradableelement allows the helix 414 to open to its full height more slowly,prolonging the equilibrium time and slowing the effect of the helicalprotrusion 440 on the contacting tissue.

A drawstring (not shown) that runs through some or all of retrievalelements 442 can be used to withdraw the protrusions 440 from theluminal wall. Pulling on the drawstring applies a normal force directlyto the loops 412, causing the loops 412 to collapse into the coils belowto disengage the helix 414 from the surrounding tissue. As the coilscollapse, one within the next, they act as a “cheese cutter”: each coilhelps to shear the surrounding tissue from the coil above it as theabove coil passes through the lower coil, freeing the helical protrusion440 from any scar tissue that may have grown through or around the wirein the loop 412 and the helix 414. Pulling on the drawstring also causesthe anchor 102 to collapse for endoscopic withdrawal from theimplantation site as described below.

FIG. 4B shows an implant 460 with an end effect 462 at the end of eachhelical protrusion 470. In this example, each end effect 462 is a postthat is oriented in the center of a respective helical protrusion 470and protrudes slightly beyond the loop 412 of the respective helicalprotrusion 470. The end effects 462, which may be sharpened to engagethe contacting tissue more quickly, initiate an injury to the duodenalwall and lead the heads 412 through the duodenal wall. Because each endeffect 462 pierces the luminal wall, it initiates the injury that causesfibrotic tissue to encapsulate its associated helical protrusion 470more quickly. Quickly embedding the helical protrusion 470 is importantfor stabilizing and maintaining placement of the implant in a mobilevessel with pressurized luminal contents, such as the duodenum or otherportion of the intestines.

Implant 430 may also include a constraint 444 (not shown in FIG. 4B)threaded through the retrieval element 442 keeps the helical protrusion470 in a fully or partially collapsed state. As described above, theconstraint 444 can be a suture or biodegradable element that allows theuser to influence how quickly the helical protrusion 440 expands afterimplantation, which, in turn, affects how quickly the loop 412penetrates the luminal wall.

FIG. 5 is a perspective view of an alternative helical protrusion 510with a retrieval element 542 formed of a single wire without ahypodermic tube. The wire is coiled to form a helix 514 and a loop 512,then folded and formed into a retrieval element 542. Excess wireextending from the tail of the retrieval element 542 is trimmed and maybe sharpened to create an end effect 562. The base coil of the helix 414can be trimmed and/or bent as necessary before the projection isattached to the wave anchor 102, e.g., with a crimp 416, as shown inFIGS. 4A-4B, or using any other suitable attachment. Alternatively, thehelical protrusion can be fabricated with a post that runs up itscenter, and the post can be crimped or otherwise affixed to the anchor102. A constraint 544 threaded through the retrieval element 542 cankeep the helical protrusion 510 in a fully or partially collapsed state.As shown, constraint 544 is a suture that ties retrieval element 542 toa strut of anchor 102. The constraint 544 can be a biodegradable suturethat allows the user to influence how quickly the helical protrusion 510expands after implantation, which, in turn, affects how quickly the loop512 and end effect 562 penetrate the luminal wall.

FIGS. 6A-6C show how a helical protrusion 410 engages a luminal wall tosecure an implant 400 within the lumen. Helical protrusion 410 issimilar to helical protrusion 440 shown in FIG. 4A and, like protrusion440, may optionally include retrieval element 442 (not shown in FIG.6A). The implant 400 is inserted into the lumen in a compressed orconstrained state, with the helical protrusion 410 collapsed against thecollapsed anchor 102, as shown in FIG. 6A. A biodegradable constraint644 is configured to maintain the protrusion in the constrained stateuntil the constraint 644 releases. Although FIG. 6A shows protrusion 410collapsed flat against anchor 102, protrusion 410 can extend from anchor102 in the constrained state. In addition, protrusion 410 can include anend effect that extends from the anchor, such as end effect 562 shown inFIG. 5.

Releasing the helical neck 414 allows the helical neck 414 to expand,causing a tent 603 to form in the duodenal wall 601, as shown in FIG.6B. As the neck 414 continues to expand against the duodenal wall 601,it pushes the loop 412 through wall 601, as shown in FIG. 6C. Scartissue 607 forms about and possibly through the loop 412 and neck 414.Without being bound by any particular theory, initial studies suggestthat helical necks 414 tend to encourage more fibrotic encapsulationthan straight necks of similar height because helical necks have morewire in contact with the tissue.

The compliance of the helical neck 414 affects how quickly the loop 412penetrates the luminal wall 601. Initial studies suggest that thetop-most coils in the helical neck 414 continue to push through tissueafter initial contact until the contacting tissue and helix 414 come toequilibrium. If the helical neck 414 is as compliant as the luminalwall, however, then the neck 414 will not be able to push the loop 412through the luminal wall 601. Since the compliance of the helical neck414 is largely a function of wire diameter and pitch, increasing eitherthe wire diameter or the pitch the wire diameter generally increases therigidity of helical neck 414. Increasing the wire diameter too much maymake it difficult to form the wire into tight loops to shape the loop412. Wire with a diameter in the range of about 0.016 inch to about0.040 inch is generally suitable for helical protrusions 410. Nitinolwire with a diameter of about 0.019″ offers a balance: it can be formedinto tight bends for the end of the helical neck 414 and the loop 412,yet forms a helix that is stiffer than the luminal wall 601. It can alsobe packed into a capsule for endoscopic delivery. The diameter of thehelix 414 can also be varied to further customize the transition instiffness and tissue response.

Although FIGS. 4-6 show a helix 414 with a linear transition betweensuccessive coil diameters, alternative helixes can have other shapes,including parabolic profiles, cylindrical profiles, hourglass profiles,and conical profiles (e.g., with the vertex of the cone connected to theanchor). Alternatively, the helix 414 can be formed in a flattened coilthat is narrow at the center and flares out from the center into a flatspiral shape. The helix 414 could also be formed of a post thatterminates in a coil with its wrappings aligned or angled with respectto one another in a corkscrew-like fashion. Compared to otherthree-dimensional shapes, tapered shapes tend to be easier to disengagefrom a mating surface. Parabolic shapes transition more quickly fromlarge coils to small coils, facilitating a lower profile protrusion.Similarly, transitions between coils or wraps in the helix 414 can becustomized as desired. For example, the coils in the helix 414 can besized such that each coil fits into the coil below. This sizing ofsuccessive coils facilitates a lower profile for packing into thedelivery catheter and facilitates disengagement from the duodenal wall.

Compliance Measurements

The compliance/stiffness of the protrusions disclosed herein can becharacterized, in part, by the force required to deflect the protrusionsfrom their respective relaxed (extended) states towards their respectivecollapsed states. For a protrusion with a straight neck (e.g.,protrusion 110 of FIGS. 2A-2C), compliance may be defined, in part, bythe normal force required to deflect the protrusion at room temperatureby a given amount towards the strut of the collapsible anchor.Measurement shows that applying a force of at least about 0.1 lbf normalto the head (i.e., parallel to the long axis of the lumen) completelycollapses a straight-necked protrusion made of 0.010-inch diameternitinol wire, with a total length of 13 mm, ending in a loop formed oftwo wraps of wire with an inner diameter of about 3 mm. Similarmeasurement shows that applying about 0.8 lbf normal to the headdeflects the head by about 0.250 inch for a straight-necked protrusionmade of 0.020-inch diameter nitinol wire, with a total length of 11.5mm, ending in a loop formed of two wraps of wire with an inner diameterof about 3 mm. Other straight-necked protrusions may be deflected byabout 0.250 inch from their relaxed positions by forces within a rangeof about 0.80 lbf to about 0.95 lbf.

The compliance of a helical protrusion can be characterized, in part, bymeasuring the force required to (partially) collapse the helicalprotrusion at room temperature. Measurement shows that applying a forcenormal to the long axis of a helical protrusion within a range of about0.19 lbf to about 1.75 lbf, or, more preferably, about 0.32 lbf to about0.95 lbf, collapses the protrusion by about 0.250 inch, depending on thewire diameter, coil pitch, and coil size:

TABLE 1 Normal force applied to compress nitinol helical protrusions by0.250 inch at room temperature Protrusion Base Coil Top Coil Coil WireNormal Height Diameter Diameter Spacing Diameter Force 10 mm 6 mm 3 mm2.4 mm 0.016″ 0.19 lbf  6 mm 6 mm 3 mm 4.0 mm 0.023″ 0.32 lbf 10 mm 6 mm3 mm 2.4 mm 0.028″ 0.95 lbf 10 mm 6 mm 3 mm 2.4 mm 0.030″ 1.75 lbfIn addition to the compliance of the helix as measured in the normalforce to compress the helix, resistance to bending must be considered.Helix stiffness can also be characterized by the force required todeflect the helix sideways, i.e., in the plane normal to the long axisof the helix. A balance must be struck between compressability andrigidity. Deflecting a nitinol helical protrusion with a 6 mm height, 6mm base coil diameter, 3 mm top coil diameter, 4.0 mm coil spacing, and0.020-inch wire diameter sideways by 0.250 inch at room temperaturetakes a force of at least about 0.033 lbf. Increasing the wire diameterto about 0.028 inch increases the force to about 0.135 lbf for a0.250-inch deflection at room temperature. A preferred balance can bedefined within the specifications above.Bidirectional and Compound Barbs

FIGS. 7A, 7B and 7D show compound barb protrusions 710 in constrainedstates, the protrusions 710 being maintained in the constrained statesby respective biodegradable constraints 744. FIG. 7C shows a compoundbarb protrusion 710 in an un-constrained state, for example after therelease of the constraint 744.

FIG. 7A shows protrusion 710 coupled to anchor 102 in a constrainedstate extending from the exterior surface of the anchor to a height a.Preferably, the height a to which the protrusion extends from anchor 102is at least about 2 mm, e.g., between about 2 mm and about 4 mm. Theprojection height a is measured from an exterior surface of the anchorto the tip or end 713 of a leg 114 of protrusion 710. In anunconstrained state, protrusion 710 extends further from the exteriorsurface of the anchor, as described with reference to FIG. 7C below.

As shown in FIG. 7A, protrusion 710 is a bidirectional barb thatincludes two tines or legs 714 with ends directed in opposite directionsfrom each other and outwardly from the anchor 102, of which one tine isso oriented at an oblique angle as to prevent longitudinal movement ofthe implant in a first direction and another tine is so oriented at anoblique angle as to prevent longitudinal movement of the implant in asecond direction substantially opposite to the first direction. Asshown, the oblique angles of the two legs 714 may be the same angle α.The angle α and the length of leg 714 determine the projection height a.In a constrained state, a portion of protrusion 710, e.g. segment 715 bof leg 714, may extend outward from the anchor 102 at an angle α ofbetween about 30 degrees to about 50 degrees, preferably at about 41degrees. The barb protrusion 710 may include a sharp point at the end713 of leg 714 to pierce tissue and provoke an inflammatory response.

A biodegradable constraint 744 is configured to maintain the protrusionin the constrained state until the constraint releases. Biodegradableconstraint 744 can be made from any suitable biodegradable material asdescribed herein. Constraint 744 can cover a portion of protrusion 710and may also cover a portion of anchor 102. In one embodiment,constraint 744 is a bioresorbable tube formed from PLGA that covers amid-portion of protrusion 710 and a strut of anchor 102. The PLGA tubemaintains the protrusion 710 in a constrained state, extending from theanchor 102 at a height a, until the tube dissolves. Height a may be atleast about 2 mm, or between about 2 mm and 4 mm.

Preferably, protrusion 710 is a bidirectional barb constructed of ashape memory alloy (e.g., Nitinol or similar) with a compound angleshape set into the barb. A releasable restraining mechanism, such asbiodegradable constraint 744, allows the compound barb to change heightover a predetermined period of time in the body. The compound shape ofthe barb protrusion is best described with reference to FIG. 7C.

As shown in FIG. 7C, the protrusion 710 includes a first segment 715 aproximate the anchor 102 that extends from the anchor 102 along a firstaxis. The first segment 715 a and anchor 102 form an angle α, the end ofthe first segment that is distal to the anchor being at a height a fromthe exterior surface of the anchor. Protrusion 710 also includes asecond segment 715 b that extends from the first segment 715 a along asecond axis oriented at an oblique angle β to the first axis. Thecombination of the lengths of the segments 715 a and 715 b and theangles α and β result in the protrusion to extend from the surface ofanchor 102 at a height b. In one example, protrusion 710 extends to aheight b of between about 4 mm and about 8 mm when released from theconstrained state. In an un-constrained or relaxed state, a portion ofprotrusion 710, e.g. segment 715 a, may extend outward from the anchor102 at a combined angle of between about 41 degrees and about 90degrees, preferably at an angle of about 82 degrees.

In the constrained state shown in FIG. 7A, the first axis is alignedwith surface of the anchor 102 and first segment 715 a is collapsedagainst anchor 102. In the constraint state, the first segment 715 a ofprotrusion 710 may be covered in whole or in part by biodegradableconstraint 744. In the example shown in FIG. 7A, the protrusion 710 is abidirectional barb having two legs 714 of equal length that are formedsymmetrically bout a mid-point of the protrusion. At the mid-point, theprotrusion is connected to anchor 102 with crimp 716 or other suitableconnection. Biodegradable constraint 744 covers crimp 716 and segments715 a of symmetrically formed legs 714. The legs 714, however, need notbe of equal length or symmetrically formed, nor need the biodegradableconstraint 744 cover the midpoint of the protrusion 710 or cover theprotrusion 710 in a symmetric configuration. In some embodiments,multiple constraints are used to keep the protrusion in a constrainedstate.

FIG. 7B shows protrusion 710 as in FIG. 7A, except that two constraints744 are used to separately tie the two legs 714 of protrusion 710 toanchor 102. Each of the constraints 744 holds one leg 714 of theprotrusion 710 in a constrained state. The two constraints 744 may beengineered to degrade at about the same of a different period of timeafter the protrusion has been implanted in the lumen. As shown in FIG.7B, constraints 744 can be tubes, for example formed from PLGA polymer,that wrap around legs 714 and anchor 102.

FIG. 7D shows protrusion 710 as in FIG. 7A, except that two sets ofconstraints 744 are used to separately fix the two legs 714 ofprotrusion 710 to anchor 102. Each of the constraints 744 holds one leg714 of the protrusion 710 in a constrained state. The two sets ofconstraints 744 may for example be bioresorbable sutures that can beengineered to degrade at about the same of a different period of timeafter implantation. For example, by configuring individual sutures todegrade at different times, a user can control the incremental releaseof protrusion 710 from the initial constrained state shown in FIG. 7D.In his way, the protrusion 710 can be inserted into the lumen in aninitial constrained state and at an initial height a, and thereafterallowed to incrementally extend further from anchor 102 as theconstraints 744 incrementally release.

FIGS. 8A-8B illustrate how the tissue responds to an implant 800 havinga conventional barb 810 penetrating the wall of the gastrointestinaltract. FIG. 8A shows implant 800 having barb 810 engaging the luminalwall 801, 803 in an initial conditional after deployment into the lumen.Barb 810 is coupled to anchor 102 of implant 800 with crimp 816. Barb810 has tines 814 that have pierced the mucosa 803 and the muscle layer801 of the luminal wall. The mucosa 803 is relatively soft tissue, whilethe muscle layer 801 is relatively tough tissue. FIG. 8B shows implant800 after tissue remodeling has taken place over a period of time afterimplantation. As described above, the body's healing response stimulatesa progressive tissue proliferation around the barb 810 in response tothe injury caused as the anchor 102 pushes the tines 814 of barb 810into the wall of the duodenum. The inflammatory response to the injurycauses thickening of the duodenal wall over time resulting in the tines814 of barb 810 disengaging from the tissue. Typically, the thickeningof the duodenal wall is the result of infiltration of less stable,granulation tissue 805, such that the tissue closest to the lumen is notvery tough or stable. Tougher tissues, such as the muscle layer 801 andthe scar tissue that forms around the barb ends, remodel at a distance.The thickening of the wall leads to the barb 810 disengaging from themuscle layer 801 or the fibrotic scar tissue while still residing in theless stable, granulation tissue 805 and mucosa 803. As barb 810separates from the duodenal wall, the implant 800 may become unstableand migrate or rotate within the duodenum.

FIGS. 8C-8D illustrate how tissue responds to an implant 700 having acompound barb 710 penetrating the wall of the gastrointestinal tract andfurther extending upon release of a biodegradable restraints 744. FIG.8C shows implant 700 having protrusion 710 engaging the luminal wall801, 803 in an initial conditional after deployment into the lumen.Protrusion 710 is a compound barb protrusion as described above withreference to FIGS. 7A-C. Protrusion 710 is coupled to anchor 102 ofimplant 700 with crimp 716. As shown in FIG. 8C, two biodegradableconstraints 744 keep protrusion 710 in a constrained state for initialdeployment. Protrusion 710 has tines or legs 714 that extend from theanchor 102 and that have pierced the mucosa 803 and the muscle layer 801of the luminal wall. The use of biodegradable constraints 744 thatdissolve in the duodenum over a period of time, e.g. 1-3 months, allowsthe compound barb protrusion 710 to extend between about 2 mm and about4 mm from the anchor 102 when placed in the duodenum, and then extendfurther when the constraints have dissolved. For example, the protrusion710 may extend to between about 4 mm and 8 mm when released from theconstrained state.

FIG. 8D shows implant 700 after remodeling of the tissue and afterrelease of biodegradable constraints 744. As in the case of theconventional barb 810, thickening of the luminal wall has occurred dueto the proliferation of tissue around the protrusion 710, including theinfiltration of granulation tissue 805 into the mucosa 803. However,release of the constraints 744 allowed protrusion 710 to expand andmaintain contact with tough muscle tissue 801 and tough scar tissue thathas formed in the muscle layer.

Deployment and Removal of Anchors Secured with Protrusions

Each of the aforementioned implants may be deployed in the intestine,preferably in the duodenum, and more preferably in the duodenal bulbjust distal to the pylorus. Typically, a doctor or other qualifiedperson inserts the implant into the intestine with an endoscopicdelivery device. During insertion, the delivery device holds the implantin a compressed state. Protrusions of the implant are also held incompressed or constrained state, for example, by a biodegradableconstrained. Once in position, the implant is released from the deliverydevice and allowed to self-expand, causing the protrusions to engage theintestinal wall. In implant with loop and neck protrusions, theexpansion of the implant cause each neck coupled to the anchor to pushits respective loop against the intestinal wall. Similar, in implantswith barbs coupled to the anchor, the expanding anchor causes the barbsto engage the intestinal wall. Some implants may include a sleevecoupled to the anchor, which can be deployed within the intestine asdescribed in U.S. Pat. No. 7,122,058; U.S. Pat. No. 7,329,285; U.S. Pat.No. 7,678,068; and U.S. patent application Ser. No. 11/057,861 (now U.S.Pat. No. 7,837,633), filed on Feb. 14, 2005, by Levine et al., all ofwhich are incorporated herein by reference in their entireties.

An implant secured with protrusions tipped with open loops or barbs maybe removed laparoscopically, surgically, or, more preferably,endoscopically with an endoscope. For example, an implant may becollapsed using a drawstring, then withdrawn from the intestine using anendoscope. Further details on endoscopic removal can be found in U.S.application Ser. No. 11/318,083, filed on Dec. 22, 2005, by Lamport andMelanson; and in U.S. application Ser. No. 12/005,049, filed on Dec. 20,2007, by Levine et al., both of which are incorporated herein byreference in their entireties.

Seals, Sleeves, and Restrictor Plates

FIGS. 9A-9B show an implant 900 that includes an anchor 902 with apolymer covering 904. In the example shown in FIG. 9A, protrusions 910projecting from the anchor 902 support open loops 912 that can be usedto create fibrotic encapsulations in the intestinal wall as describedabove. Constraints 944, such as biodegradable sutures, maintainprotrusions 910 in a constrained state. In the example shown in FIG. 9B,protrusions 1010 projecting from the anchor 902 include compound barbs1014. Constraints 1044, such as biodegradable tubing, maintainprotrusions 1010 in a constrained state. As shown in FIGS. 9A-9B, asleeve 906 is coupled to the distal side of the anchor 902 for extensioninto the intestine. The sleeve 906 may be permanently or detachablyaffixed to the anchor 902. For instance, a detachable sleeve can beendoscopically attached to or removed from a permanently orsemi-permanently secured anchor depending on treatment progress.

Typically, the sleeve 906 is floppy and conformable to the wall of theintestine when deployed. It also has a wall thickness of less than about0.001 inch to about 0.005 inch and a coefficient of friction of about0.2 or less. The polymer covering 904 and the sleeve 906 may be made ofa fluoropolymer, such as ePTFE coated or impregnated with fluorinatedethylene polyethylene (FEP), or any other suitable material. The sleeve906 and anchor covering 904 can be a single, integrally formed piece.They can also be separate pieces, depending on whether the anchor 902 ispartially or wholly uncovered, as long as the anchor 902 forms asufficiently good seal between the sleeve 906 and the stomach, pylorus,and/or intestine to funnel chyme through the sleeve 906. Each loop 912or barb 1014 remains uncovered or only partially covered to promote thein-growth of fibrotic tissue.

Anchors secured with loops and necks may also be used to securerestrictor plates within the gastrointestinal tract to treat obesity,such as the restrictor plates disclosed in U.S. patent application Ser.No. 10/811,293, filed on Mar. 26, 2004, by Levine et al.; U.S. patentapplication Ser. No. 11/330,705, filed on Jan. 11, 2006, by Levine etal.; and U.S. patent application Ser. No. 11/827,674, filed on Jul. 12,2007, by Levine et al., all of which are incorporated herein byreference in their entireties. An implant with a restrictor platetypically includes a restricting aperture that retards the outflow offood from the stomach to the intestine. The diameter of the aperture isless than 10 mm, is preferably less than 7 mm, and is more preferablyinitially in the range of about 3-5 mm. Alternatively, the aperture maybe elastic and expandable under pressure from material flowing throughthe anchor and the aperture at elevated physiological pressures; aspressure increases, the aperture opens to greater diameters. The implantmay include a sleeve that extends into the intestine.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims. For example, all or part of theprotrusions described above can be covered to further controlinteraction with contacting tissue. A bio-absorbable suture or adhesivecould be used to affix the covering to the protrusion. As thebio-absorbable material degrades or is absorbed by the body, thecovering is free to fan open, creating an added level of control ofinteraction between the protrusion and the surrounding tissue.Alternatively, the protrusion may be made from a polymer or a compositematerial, such as a non-degradable or biodegradable material. Implantscan also include different types of protrusions, e.g., any combinationof straight protrusions with open loops, helical protrusions with openloops, and pointed barbs.

What is claimed is:
 1. An implant comprising: a cylindrical, collapsible anchor to be deployed within a lumen; a protrusion coupled to the anchor, the protrusion, in a constrained state, extending from an exterior surface of the anchor to penetrate tissue and, in an unconstrained state, extending further from the exterior surface of the anchor than in the constrained state, the protrusion including a first segment proximate the anchor that extends from the anchor along a first axis, and a second segment that extends from the first segment along a second axis, the first segment, in the constrained state, being collapsed against the anchor, the first axis aligned with the surface of the anchor, and the second segment, in the constrained state, extending away from the anchor; and a biodegradable constraint configured to maintain the protrusion in the constrained state until the constraint releases.
 2. The implant of claim 1, wherein the constraint covers at least a portion of the protrusion.
 3. The implant of claim 2, wherein the covered portion of the protrusion includes a mid-portion of the protrusion.
 4. The implant of claim 2, wherein the constraint further covers at least a portion of the anchor.
 5. The implant of claim 4, wherein the constraint includes a tube.
 6. The implant of claim 4, wherein the constraint includes a suture that ties a portion of the protrusion to a portion of the anchor.
 7. The implant of claim 1, wherein the constraint degrades when exposed to water.
 8. The implant of claim 1, wherein the constraint degrades when exposed to acid.
 9. The implant of claim 1, wherein the constraint is bioresorbable.
 10. The implant of claim 1, further comprising additional biodegradable constraints, each constraint configured to maintain the protrusion in a different constrained state and to degrade over a different predetermined period after the implant has been deployed within the lumen.
 11. The implant of claim 1, wherein the protrusion is a bi-directional barb.
 12. The implant of claim 11, wherein the barb comprises two tines with ends directed in opposite directions from each other and outwardly from the anchor, of which one tine is so oriented at an oblique angle as to prevent longitudinal movement of the implant in a first direction and another tine is so oriented at an oblique angle as to prevent longitudinal movement of the implant in a second direction substantially opposite to the first direction.
 13. The implant of claim 1, wherein the protrusion is coupled to the anchor between ends of the anchor.
 14. The implant of claim 1, wherein the protrusion extends between about 4 mm and about 8 mm from the exterior surface of the anchor when released from the constrained state.
 15. The implant of claim 1, wherein the protrusion is configured to penetrate a wall of the lumen.
 16. The implant of claim 1, wherein the protrusion is formed of wire with a diameter of about 0.010 inches to about 0.040 inches.
 17. The implant of claim 1, wherein, in the constrained state, a portion of the protrusion folds against the anchor.
 18. The implant of claim 1, wherein, in the constrained state, a portion of the protrusion extends outward from the anchor at an angle of between about 30 degrees and about 50 degrees.
 19. The implant of claim 1, wherein, in the constrained state, a portion of the protrusion extends outward from the anchor at an angle of about 41 degrees.
 20. The implant of claim 1, wherein, in a relaxed state, a portion of the protrusion extends outward from the anchor at an angle of between about 41 degrees and about 90 degrees.
 21. The implant of claim 1, wherein, in a relaxed state, a portion of the protrusion extends outward from the anchor at an angle of about 82 degrees.
 22. The implant of claim 1, wherein the protrusion is formed as a unitary piece.
 23. The implant of claim 1, wherein: the second axis is oriented at an oblique angle to the first axis.
 24. The implant of claim 1, wherein, in the constrained state, the protrusion extends between about 2 mm and about 4 mm from the exterior surface of the anchor.
 25. The implant of claim 1, wherein the anchor has a relaxed diameter of at least about 40 mm.
 26. The implant of claim 1, wherein the anchor is a wave anchor.
 27. The implant of claim 1, further comprising: an unsupported, thin-walled sleeve coupled to the anchor and configured to extend into the lumen upon deployment of the collapsible anchor.
 28. The implant of claim 1, further comprising: a drawstring configured to collapse the anchor.
 29. The implant of claim 1, wherein, in the constrained state, the protrusion extends at least about 2 mm from the exterior surface of the anchor.
 30. An implant comprising: a collapsible anchor to be deployed within a lumen; a bi-directional barb coupled to the anchor, the barb, in a constrained state, extending from an exterior surface of the anchor to penetrate tissue and, in an unconstrained state, extending further from the exterior surface of the anchor than in the constrained state, the barb including a first segment proximate the anchor that extends from the anchor along a first axis, and a second segment that extends from the first segment along a second axis oriented at an oblique angle to the first axis, the first segment, in the constrained state, being collapsed against the anchor, the first axis aligned with the surface of the anchor, and the second segment, in the constrained state, extending away from the anchor; and a biodegradable constraint configured to maintain the barb in the constrained state until the constraint releases. 